The most common explanation is condensation. The waterproof coating that protects the outside of the tent also forms a barrier for moisture leaving your tent. Fully sealed tents are more likely to get condensation. To remove condensation simply open your tents ventilation panels and door whenever possible.
It is also possible you might have a leak or broken seal. In this case, simply check each panel and seal to find the problem.
Should you wish to discuss this further, please contact us here where a member of our team will be more than happy to assist.